Templates for Calculating Ageing
Precision
Description of Templates
Template Versions Available
How to Use the Standard Precision Template
Output
Bowker's Test of Symmetry
Pivot Tables
Contact Info
References
Description
A series of
Microsoft Office Excel* templates were
designed to automate the calculation of various measures of ageing
precision, including percent agreement and the total coefficient
of variance (CV, Chang 1982), plus generating both an age-bias
plot and an age matrix table. These measures were recommended
by Campana et al. (1995). In the standard template, symmetry
is also tested with a Bowker's test (Hoenig et al. 1995)
if the percent agreement drops below 90%.
These templates were created
in Microsoft Office Excel 2003*. Please
feel free to download and apply them as needed, and to share them
with other interested parties. As of the release date, all these
templates were correct to the best of my knowledge.
Templates are currently being tested in Microsoft Office Excel 2007*. Please use the Contact Info below to request these updates when they become available.
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Template Versions Available
Click on each filename to download
the corresponding template.
Standard precision template
Precision.xlt (1.1 Mb)
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This template is intended
to compare duplicate ages from one age reader, but can easily
be used to compare ages from two different readers as well.
It is designed for fish with a maximum age of 16 years or
less.
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Expanded precision templates
Precision25yr.xlt (1.0 Mb)
Precision30yr.xlt (1.3 Mb)
Precision50yr.xlt (1.4 Mb)
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These are designed to compare
duplicate ages for species which can live for up to 25, 30,
or 50 years. The 30- & 50-year templates do not accept
age-0 fish; the 25-year template does. The 50-year template
includes a 'forgiveness factor' for age differences ± 2
years when calculating percent agreement, and has a somewhat
different arrangement from the other files. |
Accuracy template
Accuracy.xlt (1.0 Mb)
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This template is intended
for testing age reader accuracy vs. reference collections.
It does not include a test of symmetry, as the Bowker's test
is inappropriate for cases where one age is considered to
be more reliable than the other.
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Symmetry template
Symmetry50yr.xlt (97 kb)
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This template may be used to calculate Bowker's test of symmetry if the maximum age is above 16 years (otherwise, use Precision.xlt) and there are no age differences of more than 10 years. Directions are included on the template itself.
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How To Use The Standard
Precision Template
The description that follows applies
specifically to the standard template (Precision.xlt). The other
templates are comparable, but cell positions can change from one
template to another. Information on the Bowker's test applies
only to the standard template.
Production (prod.) age is considered
to be the first age attached to a given fish, obtained while the
age reader is working with the entire set of samples (survey,
commercial quarter, etc.). Ages obtained while re-ageing fish from
the precision subsample are labeled 'test ages.' (Note: In the
Accuracy template, reference (ref.) age is used to indicate the
known or consensus age for each fish.)
Note: All data shown in red
on the template should be replaced.
Step 1: First, the two
sets of ages must be entered in columns A (prod. age) &
B (test age), starting at row 36. Overwrite the sample ages already
listed. Fish which are omitted in either ageing run may
be listed in the table at J36, but should not be included in this
section. Blank lines in the age data must also be avoided, as
these can artificially reduce the total CV.
Note: Do not change the
first 34 rows of 'space-keeper' ages. They are included to ensure
that the Pivot Tables list all ages, which in turn allows other
calculations to refer to the correct locations.
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Step 2: Once all ages are entered,
the calculations in columns C-E (starting at row 36) must be
copied downward to the last age pair. The computer sometimes
does this automatically, depending on how the ages are entered.
These columns calculate the CV for each fish (indicated
by the subscript 'j'). Multiple columns were used in order to
simplify the equations. The column values are:
C, the average age, Xj;
D, the sum of the squared differences (SSD) between each age
and Xj; and
E, CVj, the square root of the SSDj divided by Xj.
For fish for which both ages are zero, the 'IF'
statement in column E resets the CVj to zero to avoid an error
message. This could convert blank lines in your data to artificial
CVj values of zero. To remove any blank lines, you can run the
'sort' function on both columns of ages before copying the calculations.
(Note: On the 30- and 50-year templates, any age-0 fish in columns
A or B will generate a '#ZERO!' message in column E, and the Pivot
Tables will not work properly.)
Step 3: Move to the upper right portion
of the template. Pivot Table 1 starts at cell AN1; Pivot Table
2 starts at AN23. Both Pivot Tables must be refreshed.
This can be done simply by right-clicking within each Pivot Table,
and selecting the 'Refresh Data' option. See below
for more details on Pivot Table layout.
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Note: These tables begin
in Column AZ for the 25-year template, Column BA for the 30-year
template, and Column CF for the 50-year template.
Step 4: At the top of Columns H-N, the
labels should be updated, including:
H1, the sample type (survey, commercial,
etc.) and year the fish were captured;
H2, what is compared (repeated readings of the same fish/comparison
between two readers);
N1, the species name;
N2, the date the exercise was completed; and
N3, the name of the age reader.
Add other information, such as stock area, as appropriate.
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At this point, all remaining calculations
& displays should be complete. Double-check that the total N,
CV, and other measures seem reasonable. If not, review Steps 1-3
to see if anything was overlooked.
Step 5: Save the file to a new,
distinctive filename before printing. A file name which incorporates
species, sample source, and age reader is recommended. For example,
"SJS_HD_200303_GOM.xls" would refer to an exercise which
I completed on haddock collected on the 200303 survey in the Gulf
of Maine.
Output
The printed data (H1-AL43) show the sample size,
total CV (expressed as a percentage), percent agreement, and Bowker's
test results (if appropriate; see below).
A breakdown of the average test age for each production age (with
measures of variation) is shown in both table form and in the
age-bias plot. An age matrix table is included, as well. The header
lists the document name and the date printed.
Click on the table to open in a new
window.
For much of the printout, zeroes are not shown.
Disregard any "#DIV/0!" and "#NUM!", as all
ages may not be adequately represented in your sample. Do not
attempt to remove these from the template, as the calculations
in those cells may be needed in another precision exercise.
Note: The output for the
50-year template is arranged differently, but contains the same
elements.
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Bowker's Test of Symmetry
In the standard template, the cells below the
printout (J45-AJ85) are used in calculating the Bowker's test
(Hoenig et al. 1995). This considers only the samples for
which the age was not agreed upon. Comparisons are made on the
diagonal, i.e. fish with ages of (1, 2) are compared with
fish having ages of (2, 1).
Cells S46-AJ64 calculate the chi-squared value
for each diagonal pair of ages, based on the data in the age matrix
table. Cells S67-AJ85 indicate which of these pairs include actual
fish; this total (cell K59) is the number of degrees of freedom
for the test. In cells K46-K55, the chi-squared values are summed
for each difference between the two ages (i.e. 1 year,
2 years, etc.), with an overall total in cell K58. Differences
of 10 or more years are combined in cell K55, and broken out in
cells K65-K71. Hopefully, there will be few disagreements of this
magnitude.
The results of the Bowker's test are reported
in the printout only if the percent agreement is below 90%. A
significance level of P<0.05 is used to distinguish between
significance (**) and non-significance (n/s). If the test is not
reported, these cells (P6-P9) contain 'N/A' for 'not applicable.'
Note: The standard precision
template is the only one in this set which incorporates a Bowker's
test. It is not applicable to an accuracy exercise against known-age
samples, nor are the necessary calculations conducive to inclusion
on the precision templates for long-lived species. If a symmetry test is
needed for older fish, use Symmetry50yr.xlt.
Pivot Table 1
The upper Pivot Table (AN1-AR20) calculates the
Total CV and statistics for the test ages at each production age.
The Pivot Table refers to Columns A, B, and E. Line 21 is included
to make necessary adjustments to the Pivot Table results, by accounting
for blank spaces in A2-B35. Mean CV is later calculated as (Sum
of Total CVs)/N from cells AQ21 and AR21. Part of this table is
mirrored in cells M13-N30 on the printout, as well.
Use of production age as the basis for these calculations
is arbitrary and is not meant to indicate that either set of ages
is more accurate. Either set could be used here and as the x-axis
in the age bias plot.
Pivot Table 2
The lower Pivot Table (AN23-BG43) is the basis
for the age frequency table in the printout, and the source of counts
of fish and percent agreement values by age. It refers to columns
A and B only. Again, line 44 is present to adjust the totals because
of blank spaces at the top of Columns A and B.
Contact Info
Please contact Sandy
Sutherland (Sandy.Sutherland@noaa.gov) if you need any
assistance with these templates, or would like advice in developing
your own.
References
Campana, S. E., Annand, M. C., and McMillan, J.
I. (1995). Graphical and statistical methods for determining the
consistency of age determinations. Trans. Am. Fish. Soc.
124, 131-8.
Chang, W. Y. B. (1982). A statistical method for
evaluating the reproducibility of age determination. Can. J.
Fish. Aquat. Sci. 39, 1208-10.
Hoenig, J. M., Morgan, M. J., and Brown, C. A.
(1995). Analysing differences between two age determination methods
by tests of symmetry. Can. J. Fish. Aquat. Sci. 52, 364-8.
*Disclaimer:
Any use of trade or brand names in any NEFSC publication or report
does not imply endorsement.
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